Double heterojunction light emitting diodes and laser diodes having quantum dot silicon light emitters

ABSTRACT

A direct-wafer-bonded, double heterojunction, light emitting semiconductor device includes an ordered array of quantum dots made of one or more indirect band gap materials selected from a group consisting of Si, Ge, SiGe, SiGeC, 3C-SiC, and hexagonal SiC, wherein the quantum dots are sandwiched between an n-type semiconductor cladding layer selected from a group consisting of SiC, 3C-SiC, 4H-SiC, 6H-SiC and diamond, and a p-type semiconductor cladding layer selected from a group consisting of SiC, 3C—SiC, 4H—SiC, 6H—SiC and diamond. A Ni contact is provided for the n-type cladding layer. An Al, a Ti or an Al/Ti alloy contact is provided for the p-type cladding layer. The quantum dots have a thickness that is no greater than about 250 Angstroms, a width that is no greater than about 200 Angstroms, and a center-to-center spacing that is in the range of from about 10 Angstroms to about 1000 Angstroms.

[0001] This non-provisional patent application claims the benefit ofUnited States provisional patent application serial No. 60/329,882 filedOct. 17, 2001 entitled METHOD OF MAKING SI BASED LIGHT EMITTING DIODESAND LASER DIODES, incorporated herein by reference.

FIELD OF THE INVENTION

[0002] This invention relates to the fabrication of semiconductordevices, and more specifically to the fabrication of silicon-based(Si-based) light emitting diodes (LEDs) and laser diodes (LDs) usingnano-patterning and direct wafer bonding techniques.

BACKGROUND OF THE INVENTION

[0003] As the term is used herein, direct-wafer-bonding is intended tomean a process whereby two smooth and flat surfaces are broughttogether, in physical contact, in the absence of an intermediate layeror film, and usually with the application of a uniaxial pressure, suchthat the two flat surfaces are locally attracted to each other by Vander Walls forces, so that the two flat surfaces stick or bond together.The crystallites in the two flat surfaces of a direct-wafer-bondedinterface can fuse together at elevated temperatures due to thesurface-energy-induced migration and growth, or the formation of bonds,between the two surface species.

[0004] Silicon is a semiconductor of choice for integrated circuits andelectronic devices. However, silicon has an indirect bandgap of about1.1 eV, which makes silicon a relatively inefficient light emitter.

[0005] It has been predicted that reducing the physical size of asilicon crystal in all three dimensions, to that of a quantum box or aquantum dot, forces silicon to behave as a direct bandgap material, andtherefore become suitable for optical purposes. Moreover, one can tailorthe light emission wavelength throughout the visible spectrum bychanging the physical dimensions of the silicon quantum dots (Si QDs).For example, see U.S. Pat. Nos. 5,559,822 and 5,703,896, incorporatedherein by reference.

[0006] One utility of the present invention is to fabricate a doubleheterostructure (DH) laser diode (LD). A DH LD is described in U.S. Pat.No. 3,309,553, incorporated herein by reference.

[0007] The present invention makes use of nano-patterning. The use ofbionanomasks as nanometer-scale patterning masks is described in U.S.Pat. No. 4,802,951, incorporated herein by reference.

[0008] It is believed that United States patent applications have beenfiled describing the creation of the nanodot masks, and a technique fortuning the diameter of the nanodots.

[0009] DH AlInGaP p-n diodes that are wafer bonded to GaP are typicallyused for red LEDs (see F. A. Kish et al. Appl. Phys. Lett. 64, 2839,1994), while DH InGaN p-n diodes are used for green, blue and white LEDs(see S. Nakamura and G. Fasol, The blue laser diode, Springer, Berlin,1997).

[0010] As described in the publication LONG-WAVELENGTH SEMICONDUCTORLASERS (G. P. Agrawal and N. K. Dutta, AT&T Bell Laboratories MurrayHill, N.J., Van Nostrand Reinhold, New York) it has been suggested thatsemiconductor lasers might be improved if a layer of one semiconductormaterial were sandwiched between two cladding layers of anothersemiconductor material that has a relatively wider band gap. Such adevice consisting of two dissimilar semiconductors is commonly referredto as a heterostructure laser, in contrast to single-semiconductordevices called homostructure lasers. Heterostructure lasers are furtherclassified as single-heterostructure or double-heterostructure devices,depending on whether the active region, where lasing occurs, issurrounded on one or both sides by a cladding layer of higher band gap.

[0011]FIG. 1 provides an example of a prior art double-heterojunctionsemiconductor laser 10 having typical dimensions as shown, wherein thehatched area is a thin, about 0.2 micrometer thick, active layer 11 of asemiconductor material whose band gap is slightly lower than that of thetwo surrounding cladding layers 12 and 13.

SUMMARY OF THE INVENTION

[0012] This invention uses direct-wafer-bonding as a fabrication tool tomake Si-based light emitters.

[0013] In accordance with this invention, a technique known asnano-patterning is used to fabricate, and to control the size of, anordered array or an ordered matrix of Si QDs, and direct-wafer-bondingprovides that a layer of the nano-patterned Si QDs is placed between, orintegrated into, two closely adjacent silicon carbide (SiC)cladding/contact layers or wafers, thereby forming a doubleheterostructure p-n light emitting diode.

[0014] The emission wavelength of DH devices in accordance with theinvention can be tuned from the infrared part of the spectrum into theultraviolet part of the spectrum by changing the physical size of the SiQDs.

[0015] The invention provides a method of making direct-wafer-bonded,Si-based, DH light emitting diodes (LEDs), and direct-wafer-bonded,Si-based, DH LDs, by sandwiching a layer of Si QDs between two SiCcladding layers or wafers, one SiC cladding layer being an n-typecladding layer, and the other SiC layer being a p-type cladding layer.

[0016] SiC is a wide band gap semiconductor, having a band gap energyranging from about 2.5 to about 3.2 eV, depending upon the polytype, andSiC has an index of refraction (about 2.63) that is smaller than that ofSi (about 3.44). The two SiC cladding layers within DH devices inaccordance with the invention therefore provide both electricalconfinement and optical confinement inside of the Si QDs.

[0017] DH devices in accordance with the invention consist of threedistinct semiconductor layers, respectively called (1) a wide band gap,n-type, cladding/contact layer, (2) a wide band gap, p-type,cladding/contact layer, (3) and a narrow band gap, nominally indirectband gap, active layer or region that lies between the two wide band gapcladding/contact layers.

[0018] More specifically, and in a non-limiting embodiment of theinvention, the wide band gap n-type cladding/contact layer is n-SiC, thewide band gap p-type cladding/contact layer is p-SiC, and the narrow andindirect band gap active layer comprises a plurality of Si quantum dots,each quantum dot having a thickness that is no greater than about 250Angstroms, each quantum dot having a width dimension that is no greaterthan about 200 Angstroms, and the quantum dots having a center-to-centerspacing in the range of from about 10 Angstroms to about 1000 Angstroms.At less than a critical center-to-center spacing, electrons tend totunnel between adjacent quantum dots.

[0019] Direct-wafer-bonded, Si-based, DH LEDs in accordance with thisinvention can be used for displays and for lighting purposes, whiledirect-wafer-bonded, Si-based, DH LDs in accordance with this inventionare useful for communication, storage, printing purposes andphotochemistry.

BRIEF DESCRIPTION OF THE DRAWINGS

[0020]FIG. 1 shows a prior art double-heterojunction semiconductorlaser.

[0021]FIG. 2 is a cross sectional schematic view of a Si-based DH LED ora Si-based DH LD in accordance with the invention.

[0022]FIG. 3 shows how a Si wafer is direct-wafer-bonded to a SiC waferprior to reducing the thickness of the Si wafer to no greater than about250 Angstroms.

[0023]FIG. 4 shows the assembly of FIG. 3 after the thickness of the Siwafer has been reduced.

[0024]FIG. 5 shows the assembly of FIG. 4 wherein a plurality of quantumdots have been formed in the reduced-thickness Si wafer of FIG. 4, eachof the quantum dots having a height dimension that is no greater thanabout 250 Angstroms and a width dimension that is no greater than about200.

DETAILED DESCRIPTION

[0025] With reference to FIG. 2, a Si-based DH LED or a Si-based DH LD20 in accordance with this invention includes a thin (no greater thanabout 250 Angstroms thick) layer 21 having a plurality of narrow bandgap Si QDs 22, wherein Si QD layer 21 is sandwiched between a p-type,wide band gap SiC cladding layer 23 and an n-type wide band gap SiCcladding layer 24.

[0026] DH device 20 also includes a first metal electrical contact 25and its electrical connection 26, and a second metal electrical contact27 and its electrical contact 28. Metal contacts 25 and 27 arepreferably alloyed at high temperature, for example over 1000 degreescentigrade, thus assuring good ohmic contact to the DH device 20. Nickel(Ni) can be used to form contact 25, whereas aluminum (Al), titanium(Ti) or a Al/Ti alloy can be used to form contact 27.

[0027] The two doped SiC cladding layers 23 and 24 have a wide or largeband gap and a small index of refraction, and the two cladding layers 23and 24 form a type I interface (for example see C. Weisbuch and B.Vinter, Quantum semiconductor structures, Academic Press, London, 1991,page 3) with the narrow or small band gap, thin, and active Si QD layer21, to thus insure both optical confinement and electrical confinement.

[0028] Capacitance-voltage measurements made of DH device 20 confirmthat its two SiC/Si structures (i.e. 23/21 and 24/21) indeed form twoType I interfaces that are needed for electrical confinement in a DHstructure.

[0029] While the thin and active narrow band gap Si QD layer 21 of DHdevice 20 will be described as including Si quantum dots, within thespirit and scope of the invention other materials such as Ge, a SiGealloy, a SiGeC alloy, 3C—SiC, or hexagonal SiC can be used to formquantum dot layer 21.

[0030] In addition, while cladding layers 23 and 24 will be described asbeing SiC cladding layers, other materials such as 3C—SiC, 4H—SiC,6H—SiC or diamond can be used to form cladding layers 23 and 24.

[0031] With reference to FIG. 3, in the making of FIG. 2's DH device 20,a relatively thick Si wafer 30, having a thickness 33, is firstdirect-wafer-bonded onto the surface 31 of a SiC wafer 32 which may beeither the p-type wafer 23 or the n-type wafer 24 of FIG. 2.

[0032] Prior to the direct-wafer-bonding step shown in FIG. 3, the topsurface 31 of SiC wafer 32 and the bottom surface 35 of Si wafer 30 areprocessed to produce surface characteristics that facilitate thedirect-wafer-bonding of these two wafer surfaces. That is, the twomating surfaces 31 and 35 of wafers 32 and 30 are prepared fordirect-wafer-bonding, as is well known to those skilled in the art.Generally, the two surfaces 31 and 35 must be clean, they must be flat,and these two surfaces do not contain an intermediate material such asan oxide, such that direct-wafer-bonding can be achieved.

[0033] In FIG. 4 the FIG. 3 thickness 33 of Si wafer 30 has been reducedto produce a thin slice of Si 37 that is no more that about 250Angstroms thick, this being dimension 34 of FIG. 4. As stated, SiC wafer32 of FIG. 4 can be either the n-doped cladding layer 24 of FIG. 2 orthe p-doped cladding layer 23 of FIG. 2.

[0034] In FIG. 4, the thickness 33 of FIG. 3's Si wafer 30 has beenreduced, for example by etching or by polishing the top surface 38 ofFIG. 3's Si wafer 30, to a desired thickness 34 of no more than about250 Angstroms, and preferably considerably less than 250 Angstroms.

[0035]FIG. 4's thin Si slice 37 can also be accomplished using a processknown as SMARTCUT®, a process for separating a thin membrane from a bulksubstrate, for example as described in French Patent 2,681,472 and U.S.Pat. No. 5,374,564, incorporated herein by reference.

[0036] In addition, the relatively thick Si wafer 30 of FIG. 3 can beproduced on FIG. 3's surface 31 by direct-wafer-bonding a Si SIMOX(separation by implantation of oxygen) wafer onto the surface 31 of SiCwafer 32, followed by etching the SiO₂ layer and thereby transferringthe top Si layer of the SIMOX wafer to the SiC to a thickness 34 that isno more that about 250 Angstroms. This thin Si layer is then etched toproduce the quantum dots. Such a SIMOX process makes use of high oxygendose implantation in a silicon substrate for creating in the siliconsubstrate a silicon oxide layer that separates a monocrystalline siliconfilm from the substrate.

[0037] As an alternate to the direct-wafer-bonded embodiment of FIGS. 3and 4, the relatively thin Si layer 37 of FIG. 4 can be grown on theFIG. 3 surface 31 of SiC wafer 32 to a thickness 34 that is less thanthe critical thickness, to thereby avoid stress related to defectformation in Si layer 37.

[0038] As the next step in producing DH device 20 of FIG. 2, FIG. 4'sthin Si layer 37 (now thinned to no more than about 250 Angstroms, asabove described) is patterned into a plurality of quantum dots or boxes40, as is shown in FIG. 5. The top surfaces of the plurality of quantumdots 40 all lie in a plane 41 that is spaced no more than about 250Angstroms above the plane that is formed by the surface 31 of SiC wafer32, wherein plane 41 is generally parallel to plane 31.

[0039] Quantum dots 40 are preferably controlled to have athree-dimensional size that is no greater than about 250 Angstroms byabout 200 Angstroms by about 200 Angstroms. The center-to-center spacingof quantum dots 40 is in the range of from about 10 Angstroms to about1000 Angstroms.

[0040] Quantum dots 40 are preferably produced using inductively coupledplasma (ICP) etching and metal nanodot masks that are created usingbiomolecular nanomask (bionanomask) technology (for example see T. A.Winningham, Steven G. Whipple and Kenneth Douglas, “Pattern Transferfrom a biomolecular nanomask to a substrate via an intermediate transferlayer,” J. Vac, Technol B 19(5), Sep/Oct 2001).

[0041] Using bionanomasks and ICP etching, nano-pattering of FIG. 4'sthin Si layer 37 to form FIG. 5's quantum dots 40 has been demonstratedby creating an ordered array of quantum dots 40 having about a5-nanometer (nm) diameter and having a center-to-center spacing of about22 nm.

[0042] As an alternative to the above procedure of forming the FIG. 5array of quantum dots 40, a bionanomask can be deployed on a native SiO₂layer that exists on the top surface 38 of FIG. 3's Si wafer 30, tothereby create an ordered array or mask of metal nanodots that is theinverse of the FIG. 5 array of quantum dots 40. This SiO₂ layer isremoved later, during subsequent direct-wafer-bonding of a second SiCcladding layer to the FIG. 3 assembly, thereby removing the metalnanodot mask, and thereby leaving the FIG. 5 array of quantum dots 40.

[0043] Processing-induced damage on the top and generally flat surface41 of the quantum dots 22 can be removed by chemical etching inpotassium hydroxide (KOH), or by growing and then etching off asacrificial SiO₂ layer.

[0044] As a third step in a process of making FIG. 2's DH device 20 asecond SiC cladding layer or wafer (similar to SiC wafer 32 of FIG. 3)is direct-wafer-bonded to the top surface 41 of the quantum dots 40shown in FIG. 5 (i.e. to the two-layer SiC/Si QD structure shown in FIG.5), thus completing the three-layer SiC/Si-QD/SiC p-n structure 20 thatis shown in FIG. 2.

[0045] Passivation of the FIG. 2 device can then be achieved usingthermal or deposited oxides.

[0046] The interface between FIG. 2's SiC cladding layer 23 and Siquantum dots 22, and the interface between SiC cladding layer 24 and Siquantum dots 22, can include both polarities (Si—C or Si—Si), and wafers23 and 24 can be wafers that are cut on and/or off the (0001) axis.

[0047] In accordance with this invention, highly reproducible anddirect-wafer-bonding of n-type 4H—SiC and p-type 6H—SiC cladding layersto an Si QD array 21 (either undoped, pdoped, or n-doped) can beachieved, thus producing direct-wafer-bonded interfaces that have a highbond strength and high quality.

[0048] Direct-wafer-bonding using both polarities of SiC (Si—C andSi—Si), and using SiC wafers cut on-axis and off-axis, was also achievedin accordance with the invention.

[0049] The surface morphology and surface preparation procedures thatare used to form the above-described direct-wafer-bonded interfaces areimportant elements of the direct-wafer-bonding process. For example, theroot-mean-squared surface roughness of the two surfaces that are to bedirect-wafer-bonded should be better than about 10 Angstroms, asmeasured by atomic force microscopy, which minimal surface roughness canbe had by polishing and by in-situ hydrogen etching at high temperatures(above 1000 degrees centigrade). Growing an oxide on the two surfacesthat are to be direct-wafer-bonded, and subsequently etching the oxideoff of these two surfaces in hydrofluoric acid, also improves themorphology of the two surfaces.

[0050] A key issue when direct-wafer-bonding SiC and Si for verticaldevice structures such as shown in FIG. 2 is that both of thesesemiconductor materials readily oxidize in air. This oxide needs to beremoved, and thus the direct-wafer-bonding should take place in an inertor a reducing atmosphere.

[0051] Standard surface preparation prior to direct-wafer-bondingincludes the use of sacrificial oxides followed by solvent, RCA, (see W.Kern, D. A. Puotinen RCA Review, page 187, June 1970) and hydrofluoricacid cleaning.

[0052] DH devices in accordance with the invention weredirect-wafer-bonded using both hydrophilic and hydrophobic surfaces.

[0053] Direct-wafer-bonding was performed using an all-graphite waferbonder that provided chemical stability and uniform thermal expansion athigh temperatures, and that provided a way in which to apply knowncalibrated and uniaxial pressures to the two wafers to bedirect-wafer-bonded.

[0054] By way of example, direct-wafer-bonding was accomplished byapplying a pressure up to about 600 psi and annealed for up to about 60minutes at from about 700 degrees centigrade to about 1000 degreescentigrade in both inert (nitrogen and argon) and reducing atmospheres(forming gas), to thereby solidify the direct-wafer-bond.

[0055] This invention has been described in detail while makingreference to preferred embodiments of the invention. However, it isknown that others skilled in the art will, upon learning of theinvention, readily visualize yet other embodiments that are within thespirit and scope of the invention. Thus, this detailed description isnot to be taken as a limitation on the spirit and scope of theinvention.

What is claimed is:
 1. A double heterojunction light emitting device,comprising: an n-type semiconductor cladding layer selected from a groupconsisting of SiC, 3C—SiC, 4H—SiC, 6H—SiC and diamond; said n-typecladding layer having an outer surface and having a first generally flatsurface; a plurality of quantum dots formed of one or more indirect bandgap materials selected from a group consisting of Si, Ge, SiGe, SiGeC,3C—SiC, and hexagonal SiC on said first generally flat surface; each ofsaid quantum dots having a thickness measured generally perpendicular tosaid first generally flat surface that is no greater than about 250Angstroms; said plurality of quantum dots defining a second generallyflat surface that is spaced from and generally parallel to said firstgenerally flat surface; a p-type semiconductor cladding layer selectedfrom a group consisting of SiC, 3C—SiC, 4H—SiC, 6H—SiC and diamond; saidp-type cladding layer having an outer surface and having a thirdgenerally flat surface that is direct-wafer-bonded to said secondgenerally flat surface; a first metal contact on said outer surface ofsaid n-type cladding layer; and a second metal contact on said outersurface of said p-type cladding layer.
 2. The light emitter of claim 1wherein said first metal contact is Ni and wherein said second metalcontact is an Al/Ti alloy.
 3. The light emitter of claim 1 wherein saidplurality of quantum dots form an ordered array of quantum dots, eachquantum dot have a dimension measured parallel to said second generallyflat surface that is no greater than about 200 Angstroms, and saidplurality of quantum dots having a center-to-center spacing in a rangeof from about 10 Angstroms to about 1000 Angstroms.
 4. The light emitterof claim 1 wherein said n-type cladding layer is SiC, wherein saidp-type cladding layer is SiC, wherein said quantum dots are doped orundoped.
 5. The light emitter of claim 4 wherein said first metalcontact is Ni and wherein said second metal contact is an Al/Ti alloy.6. The light emitter of claim 5 wherein said plurality of quantum dotsform an ordered array of quantum dots, each quantum dot having adimension measured parallel to said second generally flat surface thatis no greater than about 200 Angstroms, and said plurality of quantumdots having a center-to-center spacing in a range of from about 10Angstroms to about 1000 Angstroms.
 7. The light emitter of claim 1wherein said n-type cladding layer is 4H—SiC, wherein said p-typecladding layer is 6H—SiC, wherein said quantum dots are doped orundoped.
 8. The light emitter of claim 7 wherein said first metalcontact is Ni and wherein said second metal contact is an Al/Ti alloy.9. The light emitter of claim 8 wherein said plurality of quantum dotsform an ordered array of quantum dots, each quantum dot having adimension measured parallel to said second generally flat surface thatis no greater than about 200 Angstroms, and said plurality of quantumdots having a center-to-center spacing in a range of from about 10Angstroms to about 1000 Angstroms.
 10. The light emitter of claim 1wherein said plurality of quantum dots are formed by growing a layer ofsaid indirect band gap material on said first generally flat surface toa thickness no greater than about 250 Angstroms, followed by formingsaid plurality of quantum dots by removing portions of said grown layer.11. The light emitter of claim 10 wherein said first metal contact is Niand wherein said second metal contact is an Al/Ti alloy.
 12. The lightemitter of claim 11 wherein said plurality of quantum dots form anordered array of quantum dots, each quantum dot having a dimensionmeasured parallel to said second generally flat surface that is nogreater than about 200 Angstroms, and said plurality of quantum dotshaving a center-to-center spacing in a range of from about 10 Angstromsto about 1000 Angstroms.
 13. The light emitter of claim 1 wherein saidplurality of quantum dots are formed by direct-wafer-bonding arelatively thick wafer of said indirect band gap material or materialsonto said first generally flat surface, followed by reducing a thicknessof said wafer to no greater than about 250 Angstroms, followed byforming said plurality of quantum dots by removing portions of thereduced-thickness wafer.
 14. The light emitter of claim 13 whereinprocessing-induced damage on said second generally flat surface of saidquantum dots is removed by chemical etching in potassium hydroxide. 15.The light emitter of claim 13 wherein processing-induced damage on saidsecond generally flat surface of said quantum dots is removed bysacrificial oxidation or by chemical etching.
 16. The light emitter ofclaim 15 wherein said first metal contact is Ni and wherein said secondmetal contact is an Al/Ti alloy.
 17. The light emitter of claim 16wherein said plurality of quantum dots form an ordered array of quantumdots, each quantum dot having a dimension measured parallel to saidsecond generally flat surface that is no greater than about 200Angstroms, and said plurality of quantum dots having a center-to-centerspacing in a range of from about 10 Angstroms to about 1000 Angstroms.18. A method of making a double heterojunction light emittingsemiconductor device, comprising the steps of: providing an n-typesemiconductor cladding layer selected from a group consisting of SiC,3C—SiC, 4H—SiC, 6H—SiC and diamond; said n-type cladding layer having anouter surface and a first generally flat surface; providing a pluralityof quantum dots on said first generally flat surface; said quantum dotsbeing formed of one or more indirect band gap materials selected from agroup consisting of Si, Ge, SiGe, SiGeC, 3C—SiC, and hexagonal SiC, eachof said quantum dots having a thickness measured generally perpendicularto said first generally flat surface that is no greater than about 250Angstroms, and said plurality of quantum dots defining a secondgenerally flat surface that is spaced from and generally parallel tosaid first generally flat surface; processing said second generally flatsurface to produce surface-characteristics that are compatible withdirect-wafer-bonding; providing a p-type semiconductor cladding layerselected from a group consisting of SiC, 3C—SiC, 4H—SiC, 6H—SiC anddiamond; said p-type cladding layer having an outer surface and having athird generally flat surface; processing said third generally flatsurface to produce a surface-characteristic that is compatible withdirect-wafer-bonding; direct-wafer-bonding said second generally flatsurface to said third generally flat surface; providing a first metalcontact on said outer surface of said n-type cladding layer; andproviding a second metal contact on said outer surface of said p-typecladding layer.
 19. The method of claim 18 wherein said first metalcontact is Ni and wherein said second metal contact is an Al/Ti alloy.20. The method of claim 18 wherein said plurality of quantum dots forman ordered array of quantum dots, each quantum dot having a dimensionmeasured parallel to said second generally flat surface that is nogreater than about 200 Angstroms, and said plurality of quantum dotshaving a center-to-center spacing in a range of from about 10 Angstromsto about 1000 Angstroms.
 21. The method of claim 18 wherein said n-typecladding layer is SiC, and wherein said p-type cladding layer is SiC.22. The method of claim 21 wherein said plurality of quantum dots forman ordered array of quantum dots, each quantum dot have a dimensionmeasured parallel to said second generally flat surface that is nogreater than about 200 Angstroms, and said plurality of quantum dotshaving a center-to-center spacing in a range of from about 10 Angstromsto about 1000 Angstroms.
 23. The method of claim 20 wherein said n-typecladding layer is 4H—SiC, and wherein said p-type cladding layer is6H—SiC.
 24. The method of claim 23 wherein said plurality of quantumdots form an ordered array of quantum dots, each quantum dot having adimension measured parallel to said second generally flat surface thatis no greater than about 200 Angstroms, and said plurality of quantumdots having a center-to-center spacing in a range of from about 10Angstroms to about 1000 Angstroms.
 25. The method of claim 20 whereinsaid step of providing a plurality of quantum dots on said firstgenerally flat surface of said n-type cladding layer includes the stepsof: processing said first surface of said n-type cladding layer toproduce a surface-characteristic that is compatible withdirect-wafer-bonding; providing a relatively thick wafer that is formedof one or more indirect band gap materials selected from said groupconsisting of Si, Ge, SiGe, SiGeC, 3C—SiC, and hexagonal SiC; processinga first surface of said relatively thick wafer to produce asurface-characteristic that is compatible with direct-wafer-bonding;direct-wafer-bonding said first surface of said relatively thick waferto first surface of said n-type cladding layer; reducing a thickness ofsaid relatively thick wafer to no greater than about 250 Angstroms; andusing nano-pattern masking techniques to form said quantum dots in saidreduced thickness wafer.
 26. A method of making a double heterojunctionlight emitting semiconductor device comprising the steps of: providing afirst cladding layer of a first-doping selected from a group consistingof SiC, 3C—SiC, 4H—SiC, 6H—SiC and diamond; said first cladding layerhaving an outer surface and a first generally flat surface; growing asemiconductor layer of one or more indirect band gap materials selectedfrom a group consisting of Si, Ge, SiGe, SiGeC, 3C—SiC, and hexagonalSiC, on said first generally flat surface to a thickness that is nogreater than about 250 Angstroms; patterning said grown semiconductorlayer to form a plurality of quantum dots therein whose top surfacesdefine a second generally flat surface that is spaced from and generallyparallel to said first generally flat surface; processing said secondgenerally flat surface to produce surface-characteristics that arecompatible with direct-wafer-bonding; providing a second cladding layerhaving a second-doping selected from a group consisting of SiC, 3C—SiC,4H—SiC, 6H—SiC and diamond; said second cladding layer having an outersurface and having a third generally flat surface; processing said thirdgenerally flat surface to produce a surface-characteristic that iscompatible with direct-wafer-bonding; direct-wafer-bonding said secondgenerally flat surface to said third generally flat surface; providing afirst metal contact on said outer surface of said first cladding layer;and providing a second metal contact on said outer surface of saidsecond cladding layer.
 27. The method of claim 26 including the step of:removing process-induced damage from said second surface of said quantumdots.
 28. The method of claim 26 wherein said plurality of quantum dotsform an ordered array of quantum dots, each quantum dot having adimension measured parallel to said second generally flat surface thatis no greater than about 200 Angstroms, and said plurality of quantumdots having a center-to-center spacing in a range of from about 10Angstroms to about 1000 Angstroms.
 29. A method of making a doubleheterojunction light emitting semiconductor device comprising the stepsof: providing a first cladding layer having a first-doping and selectedfrom a group consisting of SiC, 3C—SiC, 4H—SiC, 6H—SiC and diamond; saidfirst cladding layer having an outer surface and a generally flatsurface; providing a light-emitting semiconductor layer having athickness that is no greater than about 250 Angstroms, having a firstsurface, and having a second surface; said light-emitting layer beingformed of one or more indirect band gap materials selected from a groupconsisting of Si, Ge, SiGe, SiGeC, 3C—SiC, and hexagonal SiC;direct-wafer-bonding said first surface of said light-emittingsemiconductor layer to said generally flat surface of said firstcladding layer; patterning said light-emitting semiconductor to form aplurality of quantum dots therein; providing a second cladding layerhaving a second-doping and selected from a group consisting of SiC,3C—SiC, 4H—SiC, 6H—SiC and diamond; said second cladding layer having anouter surface and having a generally flat surface; direct-wafer-bondingsaid generally flat surface of said second cladding layer to said secondsurface of said light-emitting semiconductor layer; providing a firstmetal contact on said outer surface of said first cladding layer; andproviding a second metal contact on said outer surface of said secondcladding layer.
 30. The method of claim 29 including the step of:removing process-induced damage from said second surface of said quantumdots.
 31. The method of claim 29 wherein said plurality of quantum dotsform an ordered array of quantum dots, each quantum dot having adimension measured parallel to said second generally flat surface thatis no greater than about 200 Angstroms, and said plurality of quantumdots having a center-to-center spacing in a range of from about 10Angstroms to about 1000 Angstroms.
 32. A double heterojunction lightemitting semiconductor device comprising: a first layer having afirst-doping and selected from a group consisting of SiC, 3C—SiC,4H—SiC, 6H—SiC and diamond; said first layer having an outer surface anda generally flat surface; a light-emitting semiconductor layer having athickness that is no greater than about 250 Angstroms, having a firstsurface, and having a second surface; said light-emitting semiconductorlayer being formed of one or more indirect band gap materials selectedfrom a group consisting of Si, Ge, SiGe, SiGeC, 3C—SiC, and hexagonalSiC, and said light-emitting semiconductor layer having a plurality ofquantum dots therein; said first surface of said light-emittingsemiconductor layer physically engaging said generally flat surface ofsaid first layer; a second layer having a second-doping and selectedfrom a group consisting of SiC, 3C—SiC, 4H—SiC, 6H—SiC and diamond; saidsecond layer having an outer surface and having a generally flatsurface; said generally flat surface of said second layer beingdirect-wafer-bonded to said second surface of said light-emittingsemiconductor layer; a first metal contact on said outer surface of saidfirst layer; and a second metal contact on said outer surface of saidsecond layer.
 33. The double heterojunction light emitting semiconductordevice of claim 32 wherein said plurality of quantum dots form anordered array of quantum dots, each quantum dot having a dimensionmeasured parallel to said second generally flat surface that is nogreater than about 200 Angstroms, and said plurality of quantum dotshaving a center-tocenter spacing in a range of from about 10 Angstromsto about 1000 Angstroms.
 34. The double heterojunction light emittingsemiconductor device of claim 32 wherein said first surface of saidlight-emitting semiconductor layer is direct-wafer-bonded to saidgenerally flat surface of said first layer.
 35. The doubleheterojunction light emitting semiconductor device of claim 34 whereinsaid plurality of quantum dots form an ordered array of quantum dots,each quantum dot having a dimension measured parallel to said secondgenerally flat surface that is no greater than about 200 Angstroms, andsaid plurality of quantum dots having a center-to-center spacing in arange of from about 10 Angstroms to about 1000 Angstroms.